This invention relates to an additive layer fabrication (ALF) method, that is to say a method in which successive layers of material are added on top of each other so as to build-up a three-dimensional structure. The invention is particularly but not exclusively applicable to selective laser melting, and may be applied both to the manufacture of new articles, or to the repair of used ones.
In selective laser melting a laser beam is used to melt a controlled amount of powdered (usually metallic) material on a substrate, so as to form a layer of fused material thereon. By moving the laser beam relative to the substrate along a predetermined path, the layer can be defined in two dimensions on the substrate, the width of the layer being determined by the diameter of the laser beam where it strikes the substrate. Repeating the movement of the laser along all or part of its path enables further layers of material to be deposited, thereby fabricating a three-dimensional object.
Selective laser melting hitherto has been performed using continuous wave (CW) lasers, typically Nd:YAG lasers operating at 1064 nm. This can achieve high material deposition rates particularly suited for repair applications or where a subsequent machining operation is acceptable in order to achieve the finished component. The method does not however lend itself to the production of near-net-shape components to close tolerances and with a high quality surface finish. Preferred embodiments of one aspect of the present invention seek to address this shortcoming.